Dynamical Response Comparison Between Variable Speed and Synchronous Speed Pumped-Storage Units in Turbine Mode

Doubly-fed variable speed pumped-storage unit (VSPS) has been proposed as an alternative to the traditional synchronous speed pumped-storage unit (SSPS) due to its advantages of wide operation range and high efficiency, etc. The VSPSs can be divided into two types, i.e., Type-I unit and Type-II unit, from the perspective of control structure. Currently, among the above- mentioned three types of pumped-storage units (PSUs), the SSPS is widely applied because of its mature technology, and the Type-Ⅰ VSPS is widely adopted due to its fast power response capability. However, the Type-II VSPS was never built and put into commission, and no article or technical report reveals or explains the reasons behind it. Till now, the technical performances of the three types of PSUs connected to the power grid have not been fully investigated and compared, and the advantages and disadvantages of these PSUs in power control-related scenarios are still not clear. In addition to that, the applicability of these PSUs in different renewable energy penetration level scenarios is not yet known. In this article, comprehensive and comparative evaluations of the dynamic responses and the technical performances of the Type-Ⅰ and Type-Ⅱ VSPSs, and the SSPS, are conducted. The similarities and differences in the control structure of these PSUs are comparatively analyzed. The dynamic behaviors of these PSUs regarding frequency response, dispatch response, wind power response, etc., are evaluated. The performance of the PSUs in terms of power control for mitigating frequency fluctuations owing to the high penetration wind power variations is assessed, and the regulation capability of these units to stabilize the power grid is investigated. The performance advantages and disadvantages of the three types of PSUs in several common and important scenarios are revealed. Finally, the above analysis and comparisons were conducted and validated by using the time domain simulations and experimental methods.